An image display device referred to also as a matrix electron emitter display takes an intersection of electrode groups orthogonal to each other as a pixel, and provides an electron emission element on each pixel, and by adjusting an applied voltage (amplitude of applied voltage) or a pulse width of an applied voltage pulse to each electron emission element, amount of emitted electrons is adjusted, and the emitted electrons are accelerated in vacuum, and after that, and bombarded onto or irradiated at the phosphor, thereby to allow the phosphor of the bombarded portion to emit light. As the electron emission elements, there are those such as using a field emission type cathode, a MIM (Metal-Insulator-Metal) cathode, a carbon-nanotube cathode, a diamond cathode, a surface conduction electron emitter element, a ballistic electron surface-emitting cathode, and the like. Thus, the matrix electron emitter display denotes a cathode luminescent flat-panel display that combines the electron emission element and the phosphor.
FIG. 1 is a schematic view showing a cross section of the matrix electron emitter display. As shown in FIG. 1, in the matrix electron emitter display, a cathode plate 601 disposed with the electron emission-element and a phosphor plate 602 formed with a phosphor are disposed facing with each other. In order that the electron emitted from an electron emission element 301 reaches the phosphor plate to excite the phosphor to emit light, a space surrounded by the cathode plate, the phosphor plate, and a frame component 603 is kept vacuum. To withstand the atmosphere pressure from the outside, a spacer (support) 60 is inserted between the cathode plate and the phosphor plate.
The phosphor plate 602 includes an acceleration electrode 122, and the acceleration electrode 122 is applied with high voltage of approximately 3 KV to 12 KV. The electrons emitted from the electron emission element 301 are accelerated by this high voltage, and after that, are bombarded onto or irradiated at the phosphor, thereby exciting the phosphor to emit light.
The electron emission element used for the matrix electron emitter display includes a thin film electron emitter. The thin film electron emitter has a structure laminating a top electrode, an electron acceleration layer, and a base electrode, and includes a MIM (Metal-Insulator-Metal) cathode, a MOS (Metal-Oxide-Semiconductor) type cathode, a ballistic electron surface-emitting cathode, a HEED (High-Efficiency Electron Emission Device) type cathode, and the like. The structure of the MIM cathode is, for example, described in Japanese Patent Application Laid-Open Publication No. 2004-363075 (Patent Document 1). The MOS type cathode uses a stacked film comprising of semiconductor and insulator for the electron acceleration layer, and for example, is described in Japanese Journal of Applied Physics, Vol. 36, Part 2, No. 7B, pp. L939-L941 (1997) (Non-Patent Document 1). The ballistic electron surface-emitting cathode uses porous silicon and the like for the electron acceleration layer, and for example, is described in Japanese Journal of Applied Physics, Vol. 34, Part 2, No. 6A, pp. L705-L707 (1995) (Non-Patent Document 2). The thin film electron emitter emits the electron accelerated in the electron acceleration layer into vacuum. Further, the MIM cathode uses a metal for the top electrode and the base electrode, and uses an insulator for the electron acceleration layer, and for example, is described in IEEE Transactions on Electron Devices, Vol. 49, No. 6, pp. 1059-1065 (2002) (Non-Patent Document 3). The HEED type cathode uses a stacked layer of silicon (Si) and SiO2 for the electron acceleration layer, and for example, is described in Journal of Vacuum Science and Technologies, B, vol. 23, No. 2 (2005), pp. 682-686 (Non-Patent Document 5).
FIG. 2 is an energy band diagram showing an operation principle of the thin film electron emitter. A base electrode 13, an electron acceleration layer 12, and a top electrode 11 are stacked, and a state when a plus voltage is applied to the top electrode 11 is illustrated. In the case of the MIM cathode, as the electron acceleration layer 12, an insulator is used. By the voltage applied between the top electrode and the base electrode, an electric field is generated inside the electron acceleration layer 12. By this electric field, an electron from inside the base electrode 13 flows into the electron acceleration layer 12 by tunneling phenomenon. This electron is accelerated by the electric field in the electron acceleration layer 12, and becomes a hot electron. When this hot electron passes through the top electrode 11, a part of the electron loses energy by inelastic scattering and the like. The electron having kinetic energy larger than a work function Φ of the surface at a point of time when having reached an interface between the top electrode 11 and a vacuum (that is, the surface of the top electrode 11) is emitted from the surface of the top electrode 11 into vacuum 10. In the present specification, the current flowing between the base electrode 13 and the top electrode 11 by this hot electron is referred to as a diode current Jd, and the current emitted into vacuum is referred to as an emission current Je.
When compared with a field emission type cathode, the thin film electron emitter has characteristics suitable for the display apparatus such as strong resistance to surface contamination, small in divergence of the emitted electron beam so that a high-resolution display apparatus can be realized, small in operation voltage, the drive circuit driver at low voltage, and the like.
On the other hand, in the thin film electron emitter, only a part of the current from among the drive currents is emitted into vacuum (emission current Je). Here, the drive current is a current flowing between the top electrode and the base electrode, and is referred to also as the diode current Jd. A ratio α (electron emission ratio α=Je/Jd) of the emission current Je to the diode current Jd is approximately 0.1% to several tens %. That is, to obtain the emission current Je, the drive current (diode current) of Jd=Je/α is required to be fed to the thin film electron emitter from the drive circuit. The electron emission ratio α is referred to also as an electron emission efficiency.
In this manner, in the matrix electron emitter display using the thin film electron emitter as the electron emission element, the current to drive the element is increased. Hence, it is necessary that a current feeding capacity to the electron emission-element's electrode (in this case, it denotes the base electrode or the top electrode) from an electrode wiring is sufficiently increased.
The electron emission element used for the matrix electron emitter display includes a surface conduction electron emitter element. The surface conduction electron emitter element, for example, is described in Journal of the SID, vol. 5 (1997) pp. 345-348 (Non-Patent Document 4). The surface conduction electron emitter element, as shown in FIG. 3, provides a gap of several nanometers to several tens nanometers between a cathode electrode film 813 and an anode electrode film 811. A voltage of several tens volts is applied between the anode electrode film 811 and the cathode electrode film 813. The electron 912 emitted from the cathode electrode film 813 flows into the anode electrode film 811, and becomes the drive current Jd. A part of the electron constituting the Jd does not flow into the anode electrode film 811, but becomes an emitted electron 911, and reaches the acceleration electrode 122. The current of the emitted electron becomes an emitted current Je (since the electron is a minus charge, the direction to which the electron flows and the direction of the emission current are reversed). The electron emission ratio Je/Jd is approximately several % to ten %. In this manner, in the matrix electron emitter display using the surface conduction electron emitter element as the electron emission element, the current to drive the element is increased. Hence, it is necessary that a current feeding capacity to the electron emission-element's electrode (in this case, it denotes the anode electrode film 811 and the cathode electrode film 813) from an electrode wiring is sufficiently high.
As described above, the acceleration electrode 122 provided on the phosphor plate 602 is applied with a high voltage of approximately 3 KV to 12 KV, and the electron emitted from the electron emission element 301 is accelerated by this high voltage, and after that, is bombarded onto the phosphor. The reason why the electron is excited by high voltage of 3 KV or more is because, the higher the acceleration voltage is, the deeper the penetration depth of the electron to the phosphor is, and the luminous efficiency and life of the phosphor are increased.